1. Field of the Invention
The present invention relates to magnetic disk drive systems and more particularly to a read/write head having an aperture that allows an optical servo positioning system to read prerecorded patterns on a disk from a point between the rails of the head.
2. Description of the Prior Art
The track density of magnetic storage disks for conventional floppy disk drives is approximately forty-eight to 135 tracks per inch (TPI). In contrast, optical disk drives are capable of achieving track densities in excess of 15,000 TPI. These higher track densities are achieved through the use of closed-loop optical servos that allow a magnetic read/write head to follow data track eccentricities caused by defects in the media and outside disturbances. In rigid type magnetic disk drives, track densities of up to 1500 TPI are presently used. These drives commonly have multiple disks in which both sides are used for data. To achieve a high track density, a dedicated surface of one of the disks is set aside solely for magnetic track servo information This surface is then not usable for data storage. Thus, the total capacity of the drive is lessened. The tracking servo information is also capable of being accidentally erased causing loss of access of all data.
Various techniques have been reported for using optical means for acquiring track following servo information contained on a magnetic recording media. For example, Ahn, et al., in U.S. Pat. No. 4,633,451, issued on Dec. 30, 1986, for "Optical Servo For Magnetic Disks", disclose the use of a laser diode to read track following servo information in the form of a plurality of spots contained in an optical layer positioned above a magnetic recording layer.
DiStefano et al., in U.S. Pat. No. 4,570,191, issued on Feb. 11, 1986, for a optical sensor for servo position control, disclose a servo sensor comprising a light source and a light detector, and which is axially aligned and contained on a single semiconductor chip.
M. Johnson, in U.S. Pat. No. 4,558,383, issued on Dec. 10, 1985, for "Information Storage Disk Transducer Position Control System Using a prerecorded Servo Pattern Requiring No Alignment With the Storage Disk", discloses a servo apparatus having a sensor for detecting a pattern of spots on a surface of an information storage media. The spots comprise a dense array of substantially translation invariant marks and separate information recording tracks are detected by measuring the rate at which the spots are detected by the sensor.
J. Cocke. et al., in U.S. Pat. No. 4,587,579, issued on May 6, 1986, for "System for Position n on a Rotating Disk", disclose a servo control system comprising a detector for reading a plurality of spiral radial-position-encoding patterns on a media.
A. S. Hoagland in "Optical Servo of Magnetic Recording", IBM Technical Disclosure Bulletin, Vol. 20(10), page 4108 (March 1978), suggests a system for achieving optical servo control where a flexible disk media includes a plurality of optical servo tracks positioned underneath a magnetic layer.
D. A. Thompson. et al., in "Embossed Servo Techniques For Floppy Disks", IEEE Conference Proceedings, No. 43, p. 321 (July 1979), suggests the use of embossed marks on flexible magnetic media for obtaining non-magnetic optical or capacitive servo information.
N. Koshino and S. Ogawa in "Optical Method of the Head Positioning in Magnetic Disk Systems", preprint from IEEE Transactions on Magnetics (1980), disclose an optical head for achieving track following servo control which is mounted on the head arm and which includes an LED light source and three optical fibers for delivering light to a media. The media comprises a plurality of circular optical tracks, dyed black, and located underneath a magnetic film.
Related work has occurred in the laser video disk area, from which optical disks for digital data storage and the audio laser compact disk (CD) have evolved. Fundamentally, the optical servo information is inscribed and used in the same way for all these disks. A mastering machine is used to format optical information onto a master disk. The master is then replicated to form the actual disk used by the customer. A laser and associated optics are used to acquire the mastered servo information as well as read data from the disk. The data can be inscribed during the mastering process as with the video and audio disks or it can be written by the read/write laser as in disks for digital information storage.
A disk drive system is needed in which an optical servo sensor is able to access servo information on the surface of a floppy disk between the rails, through a light aperture in the head, where the floppy disk has been stabilized. Extraordinary effort and skill have been needed to reduce the present invention to practice. The prior art was not faced with the extremely high track densities that put such demands on the servo-positioning system that disk ripple outside the head slider becomes a major source of error, which is solved by the present invention. The combination of opposing rails and optical detection at the geometric center between them is key to succeeding at producing a high density magnetic-optical disk.
The problems in the prior art that need to be overcome include those associated with the thermal distortion of conventional media and sliders, variations in media surface finish and lubrication that vary from manufacturer to manufacturer and distortions of the industry standard media that is formed by attaching a metal hub to a MYLAR disk.